[ZEPPELIN-2230] clear bower_contents if bower.json changed
[ZEPPELIN-2230] clear bower_contents if bower.json changed

### What is this PR for?
Before travis build:
* check if any bower.json file is part of the commit range
* check if any commit message of the commit range contains "bower clear" or "clear bower"
* If one of the above, clear bower_components, npm cache clear
This should prevent breaking the build when upgrading a js lib.

### What type of PR is it?
Improvement

### Todos
* [ ] - Task

### What is the Jira issue?
[ZEPPELIN-2230](https://issues.apache.org/jira/browse/ZEPPELIN-2230)

### How should this be tested?

1. Using this version of .travis.yml, build the project once. (e.g. with nvd3 1.7.1)
2. then modify a version of js lib (e.g. nvd3), rebuild.
3. Verify the build goes through, check the build log for the message "Clearing bower_components cache".
4. Rebuild, without changing a version, but putting "bower clean" in a commit message.
5. Same as 3.

### Screenshots (if appropriate)

### Questions:
* Does the licenses files need update? No
* Is there breaking changes for older versions? No
* Does this needs documentation? Maybe for the "bower clear" trigger.

Author: Remilito <remy.gayet@gmail.com>

Closes #2111 from Remilito/ZEPPELIN-2230b and squashes the following commits:

cb9647f [Remilito] [ZEPPELIN-2230] clear bower_contents if bower.json changed or bower clear provided in commit message

sctincman/zeppelin,radicalbit/incubator-zeppelin,SachinJanani/zeppelin,joroKr21/incubator-zeppelin,mwkang/zeppelin,hkropp/incubator-zeppelin,Leemoonsoo/zeppelin,pellmont/zeppelin,openthings/zeppelin,astroshim/zeppelin,openthings/zeppelin,sctincman/zeppelin,r-kamath/incubator-zeppelin,fogbeam/zeppelin_mirror,fogbeam/zeppelin_mirror,SarunasG/zeppelin-oidc,yu74n/zeppelin,joroKr21/incubator-zeppelin,openthings/zeppelin,r-kamath/zeppelin,SarunasG/zeppelin-oidc,mwkang/zeppelin,pravin-dsilva/zeppelin,astroshim/incubator-zeppelin,wary/zeppelin,apache/zeppelin,rconline/zeppelin,volumeint/zeppelin,VipinRathor/zeppelin,openthings/zeppelin,soralee/zeppelin,Nova-Boy/zeppelin,hkropp/incubator-zeppelin,jongyoul/zeppelin,jongyoul/incubator-zeppelin,apache/incubator-zeppelin,anthonycorbacho/incubator-zeppelin,soralee/zeppelin,prabhjyotsingh/zeppelin,mwkang/zeppelin,karuppayya/zeppelin,astroshim/incubator-zeppelin,doanduyhai/incubator-zeppelin,SachinJanani/zeppelin,mwkang/zeppelin,openthings/zeppelin,benoyantony/zeppelin,YuanGunGun/zeppelin,sctincman/zeppelin,radicalbit/incubator-zeppelin,astroshim/zeppelin,mwkang/zeppelin,prabhjyotsingh/incubator-zeppelin,AlexanderShoshin/zeppelin,jongyoul/incubator-zeppelin,AlexanderShoshin/zeppelin,SarunasG/zeppelin-oidc,chilang/zeppelin,namanmishra91/zeppelin,rconline/zeppelin,sergeymazin/zeppelin,apache/incubator-zeppelin,doanduyhai/incubator-zeppelin,prabhjyotsingh/zeppelin,SarunasG/zeppelin-oidc,anthonycorbacho/incubator-zeppelin,jongyoul/zeppelin,namanmishra91/zeppelin,karuppayya/zeppelin,volumeint/zeppelin,prabhjyotsingh/incubator-zeppelin,Nova-Boy/zeppelin,Leemoonsoo/incubator-zeppelin,astroshim/incubator-zeppelin,Leemoonsoo/incubator-zeppelin,SachinJanani/zeppelin,pellmont/zeppelin,pellmont/zeppelin,r-kamath/incubator-zeppelin,r-kamath/incubator-zeppelin,sravan-s/zeppelin,r-kamath/zeppelin,YuanGunGun/zeppelin,herval/zeppelin,joroKr21/incubator-zeppelin,pravin-dsilva/zeppelin,namanmishra91/zeppelin,AlexanderShoshin/zeppelin,hammertank/zeppelin,lresende/incubator-zeppelin,sohaibiftikhar/zeppelin,datalayer/zeppelin-datalayer,fogbeam/zeppelin_mirror,datalayer/zeppelin,1ambda/zeppelin,benoyantony/zeppelin,sctincman/zeppelin,sohaibiftikhar/zeppelin,doanduyhai/incubator-zeppelin,vrlo/zeppelin,vrlo/zeppelin,soralee/zeppelin,cfries/zeppelin,vrlo/zeppelin,doanduyhai/incubator-zeppelin,YuanGunGun/zeppelin,hammertank/zeppelin,soralee/zeppelin,soralee/zeppelin,radicalbit/incubator-zeppelin,vrlo/zeppelin,AlexanderShoshin/zeppelin,tzolov/incubator-zeppelin,benoyantony/zeppelin,sravan-s/zeppelin,joroKr21/incubator-zeppelin,hkropp/incubator-zeppelin,karuppayya/zeppelin,astroshim/incubator-zeppelin,cfries/zeppelin,YuanGunGun/zeppelin,jongyoul/zeppelin,cquptEthan/incubator-zeppelin,radicalbit/incubator-zeppelin,Leemoonsoo/incubator-zeppelin,astroshim/incubator-zeppelin,sravan-s/zeppelin,volumeint/zeppelin,SachinJanani/zeppelin,pravin-dsilva/zeppelin,r-kamath/zeppelin,YuanGunGun/zeppelin,VipinRathor/zeppelin,chilang/zeppelin,herval/zeppelin,zjffdu/zeppelin,volumeint/zeppelin,prabhjyotsingh/zeppelin,hammertank/zeppelin,karuppayya/zeppelin,cquptEthan/incubator-zeppelin,jongyoul/incubator-zeppelin,herval/zeppelin,sohaibiftikhar/zeppelin,rconline/zeppelin,vipul1409/zeppelin,vipul1409/zeppelin,chilang/zeppelin,cfries/zeppelin,pravin-dsilva/zeppelin,cquptEthan/incubator-zeppelin,SachinJanani/zeppelin,yu74n/zeppelin,tinkoff-dwh/zeppelin,sohaibiftikhar/zeppelin,astroshim/zeppelin,datalayer/zeppelin-datalayer,hammertank/zeppelin,datalayer/zeppelin,zjffdu/zeppelin,benoyantony/zeppelin,wary/zeppelin,r-kamath/incubator-zeppelin,AlexanderShoshin/zeppelin,herval/zeppelin,jongyoul/zeppelin,pravin-dsilva/zeppelin,vrlo/zeppelin,vipul1409/zeppelin,1ambda/zeppelin,joroKr21/incubator-zeppelin,anthonycorbacho/incubator-zeppelin,pellmont/zeppelin,vrlo/zeppelin,zetaris/zeppelin,Leemoonsoo/zeppelin,hkropp/incubator-zeppelin,apache/incubator-zeppelin,SachinJanani/zeppelin,karuppayya/zeppelin,Leemoonsoo/incubator-zeppelin,rconline/zeppelin,Leemoonsoo/zeppelin,Leemoonsoo/zeppelin,benoyantony/zeppelin,tinkoff-dwh/zeppelin,namanmishra91/zeppelin,hkropp/incubator-zeppelin,tzolov/incubator-zeppelin,lresende/incubator-zeppelin,mwkang/zeppelin,apache/incubator-zeppelin,zjffdu/zeppelin,herval/zeppelin,1ambda/zeppelin,VipinRathor/zeppelin,vipul1409/zeppelin,Leemoonsoo/incubator-zeppelin,tinkoff-dwh/zeppelin,AlexanderShoshin/zeppelin,namanmishra91/zeppelin,datalayer/zeppelin,fogbeam/zeppelin_mirror,zetaris/zeppelin,SachinJanani/zeppelin,Nova-Boy/zeppelin,openthings/zeppelin,datalayer/zeppelin,Leemoonsoo/zeppelin,doanduyhai/incubator-zeppelin,astroshim/zeppelin,apache/zeppelin,pellmont/zeppelin,wary/zeppelin,vipul1409/zeppelin,sohaibiftikhar/zeppelin,apache/incubator-zeppelin,fogbeam/zeppelin_mirror,namanmishra91/zeppelin,astroshim/zeppelin,zetaris/zeppelin,tzolov/incubator-zeppelin,vrlo/zeppelin,vipul1409/zeppelin,VipinRathor/zeppelin,prabhjyotsingh/zeppelin,jongyoul/zeppelin,1ambda/zeppelin,wary/zeppelin,vipul1409/zeppelin,cquptEthan/incubator-zeppelin,prabhjyotsingh/incubator-zeppelin,sctincman/zeppelin,datalayer/zeppelin,wary/zeppelin,yu74n/zeppelin,lresende/incubator-zeppelin,benoyantony/zeppelin,prabhjyotsingh/zeppelin,prabhjyotsingh/incubator-zeppelin,jongyoul/zeppelin,sravan-s/zeppelin,cfries/zeppelin,anthonycorbacho/incubator-zeppelin,SarunasG/zeppelin-oidc,r-kamath/incubator-zeppelin,radicalbit/incubator-zeppelin,1ambda/zeppelin,astroshim/zeppelin,VipinRathor/zeppelin,sergeymazin/zeppelin,datalayer/zeppelin,cquptEthan/incubator-zeppelin,tinkoff-dwh/zeppelin,chilang/zeppelin,hkropp/incubator-zeppelin,pellmont/zeppelin,namanmishra91/zeppelin,yu74n/zeppelin,AlexanderShoshin/zeppelin,hammertank/zeppelin,soralee/zeppelin,r-kamath/zeppelin,VipinRathor/zeppelin,r-kamath/zeppelin,SarunasG/zeppelin-oidc,wary/zeppelin,sohaibiftikhar/zeppelin,sohaibiftikhar/zeppelin,zetaris/zeppelin,openthings/zeppelin,rconline/zeppelin,joroKr21/incubator-zeppelin,yu74n/zeppelin,Leemoonsoo/zeppelin,r-kamath/incubator-zeppelin,cfries/zeppelin,karuppayya/zeppelin,anthonycorbacho/incubator-zeppelin,datalayer/zeppelin,datalayer/zeppelin-datalayer,karuppayya/zeppelin,fogbeam/zeppelin_mirror,sergeymazin/zeppelin,doanduyhai/incubator-zeppelin,fogbeam/zeppelin_mirror,radicalbit/incubator-zeppelin,zjffdu/zeppelin,sravan-s/zeppelin,chilang/zeppelin,anthonycorbacho/incubator-zeppelin,astroshim/zeppelin,cquptEthan/incubator-zeppelin,sctincman/zeppelin,SarunasG/zeppelin-oidc,1ambda/zeppelin,mwkang/zeppelin,lresende/incubator-zeppelin,lresende/incubator-zeppelin,radicalbit/incubator-zeppelin,wary/zeppelin,apache/zeppelin,Nova-Boy/zeppelin,zetaris/zeppelin,joroKr21/incubator-zeppelin,pravin-dsilva/zeppelin,chilang/zeppelin,astroshim/incubator-zeppelin,tzolov/incubator-zeppelin,zjffdu/zeppelin,cfries/zeppelin,zjffdu/zeppelin,sravan-s/zeppelin,lresende/incubator-zeppelin,tinkoff-dwh/zeppelin,YuanGunGun/zeppelin,yu74n/zeppelin,volumeint/zeppelin,yu74n/zeppelin,chilang/zeppelin,tzolov/incubator-zeppelin,Nova-Boy/zeppelin,Leemoonsoo/zeppelin,Nova-Boy/zeppelin,Leemoonsoo/incubator-zeppelin,herval/zeppelin,zetaris/zeppelin,tzolov/incubator-zeppelin,zetaris/zeppelin,r-kamath/incubator-zeppelin,volumeint/zeppelin,lresende/incubator-zeppelin,hammertank/zeppelin,jongyoul/incubator-zeppelin,Leemoonsoo/zeppelin,sergeymazin/zeppelin,apache/zeppelin,1ambda/zeppelin,sergeymazin/zeppelin,cfries/zeppelin,pellmont/zeppelin,hammertank/zeppelin,zjffdu/zeppelin,prabhjyotsingh/zeppelin,apache/zeppelin,rconline/zeppelin,Nova-Boy/zeppelin,jongyoul/incubator-zeppelin,joroKr21/incubator-zeppelin,apache/zeppelin,r-kamath/zeppelin,pravin-dsilva/zeppelin,jongyoul/incubator-zeppelin,doanduyhai/incubator-zeppelin,sctincman/zeppelin,cquptEthan/incubator-zeppelin,sravan-s/zeppelin,sergeymazin/zeppelin,prabhjyotsingh/incubator-zeppelin,tinkoff-dwh/zeppelin,herval/zeppelin,jongyoul/zeppelin,volumeint/zeppelin,sergeymazin/zeppelin,VipinRathor/zeppelin,prabhjyotsingh/incubator-zeppelin,apache/incubator-zeppelin,apache/zeppelin,tinkoff-dwh/zeppelin,anthonycorbacho/incubator-zeppelin,YuanGunGun/zeppelin,r-kamath/zeppelin,rconline/zeppelin,prabhjyotsingh/zeppelin,soralee/zeppelin,datalayer/zeppelin-datalayer,benoyantony/zeppelin