Update install-mxnet-osx-python.sh (#8825)
Update install-mxnet-osx-python.sh (#8825)

* Update install-mxnet-osx-python.sh

Fixed handling of MXNET_TAG. If not set latest from master will be cloned to local directory. If a tag is specified, that tag will be used to clone the repository.

Tested with 
MXNET_TAG="1.0.0.rc0"

* Update install-mxnet-osx-python.sh

added following modifications:
a) added selection for reporting list of available tags
b) moved the tag selection into the introduction section

open: still need to resolve proper installation of the build version

* Update install-mxnet-osx-python.sh

Added check if mxnet was already installed on the system (e.g. pip install), as this might interfere with the attempt to download and install a new version.
Performed manual tests, all passing. This is a final commit.

* Update install-mxnet-osx-python.sh

empty change to trigger build.

* Update install-mxnet-osx-python.sh

another dummy change to fight the CI system.

leezu/mxnet,Northrend/mxnet,mbaijal/incubator-mxnet,CodingCat/mxnet,zhreshold/mxnet,navrasio/mxnet,indhub/mxnet,ForkedReposBak/mxnet,sxjscience/mxnet,dmlc/mxnet,tornadomeet/mxnet,jamesliu/mxnet,tornadomeet/mxnet,sxjscience/mxnet,ForkedReposBak/mxnet,larroy/mxnet,tlby/mxnet,CodingCat/mxnet,ptrendx/mxnet,ptrendx/mxnet,jamesliu/mxnet,zhreshold/mxnet,vikingMei/mxnet,fullfanta/mxnet,indhub/mxnet,mbaijal/incubator-mxnet,szha/mxnet,yajiedesign/mxnet,szha/mxnet,indhub/mxnet,weleen/mxnet,sxjscience/mxnet,luoyetx/mxnet,jiajiechen/mxnet,fullfanta/mxnet,yajiedesign/mxnet,leezu/mxnet,TuSimple/mxnet,jamesliu/mxnet,mbaijal/incubator-mxnet,larroy/mxnet,tornadomeet/mxnet,ForkedReposBak/mxnet,eric-haibin-lin/mxnet,reminisce/mxnet,rahul003/mxnet,jamesliu/mxnet,ptrendx/mxnet,luoyetx/mxnet,szha/mxnet,leezu/mxnet,TuSimple/mxnet,szha/mxnet,indhub/mxnet,yajiedesign/mxnet,CodingCat/mxnet,sxjscience/mxnet,yajiedesign/mxnet,precedenceguo/mxnet,ptrendx/mxnet,ForkedReposBak/mxnet,LinkHS/incubator-mxnet,navrasio/mxnet,weleen/mxnet,CodingCat/mxnet,reminisce/mxnet,indhub/mxnet,tlby/mxnet,TuSimple/mxnet,dmlc/mxnet,precedenceguo/mxnet,tlby/mxnet,jiajiechen/mxnet,reminisce/mxnet,Northrend/mxnet,tornadomeet/mxnet,jiajiechen/mxnet,larroy/mxnet,precedenceguo/mxnet,sxjscience/mxnet,larroy/mxnet,navrasio/mxnet,luoyetx/mxnet,LinkHS/incubator-mxnet,jiajiechen/mxnet,Northrend/mxnet,Northrend/mxnet,reminisce/mxnet,LinkHS/incubator-mxnet,yajiedesign/mxnet,navrasio/mxnet,reminisce/mxnet,rahul003/mxnet,zhreshold/mxnet,jiajiechen/mxnet,LinkHS/incubator-mxnet,luoyetx/mxnet,zhreshold/mxnet,weleen/mxnet,precedenceguo/mxnet,vikingMei/mxnet,DickJC123/mxnet,reminisce/mxnet,fullfanta/mxnet,zhreshold/mxnet,Northrend/mxnet,fullfanta/mxnet,LinkHS/incubator-mxnet,ForkedReposBak/mxnet,szha/mxnet,tlby/mxnet,eric-haibin-lin/mxnet,sxjscience/mxnet,larroy/mxnet,ptrendx/mxnet,TuSimple/mxnet,weleen/mxnet,eric-haibin-lin/mxnet,CodingCat/mxnet,Northrend/mxnet,tlby/mxnet,sxjscience/mxnet,reminisce/mxnet,mbaijal/incubator-mxnet,jiajiechen/mxnet,tlby/mxnet,tornadomeet/mxnet,reminisce/mxnet,ForkedReposBak/mxnet,zhreshold/mxnet,eric-haibin-lin/mxnet,reminisce/mxnet,jamesliu/mxnet,TuSimple/mxnet,TuSimple/mxnet,mbaijal/incubator-mxnet,TuSimple/mxnet,mbaijal/incubator-mxnet,zhreshold/mxnet,tlby/mxnet,indhub/mxnet,indhub/mxnet,vikingMei/mxnet,fullfanta/mxnet,TuSimple/mxnet,TuSimple/mxnet,fullfanta/mxnet,rahul003/mxnet,ptrendx/mxnet,mbaijal/incubator-mxnet,apache/incubator-mxnet,larroy/mxnet,Northrend/mxnet,precedenceguo/mxnet,precedenceguo/mxnet,tlby/mxnet,fullfanta/mxnet,reminisce/mxnet,leezu/mxnet,szha/mxnet,weleen/mxnet,ForkedReposBak/mxnet,yajiedesign/mxnet,jamesliu/mxnet,navrasio/mxnet,TuSimple/mxnet,eric-haibin-lin/mxnet,luoyetx/mxnet,weleen/mxnet,rahul003/mxnet,ptrendx/mxnet,mbaijal/incubator-mxnet,vikingMei/mxnet,szha/mxnet,jamesliu/mxnet,navrasio/mxnet,eric-haibin-lin/mxnet,tlby/mxnet,eric-haibin-lin/mxnet,rahul003/mxnet,weleen/mxnet,indhub/mxnet,navrasio/mxnet,yajiedesign/mxnet,rahul003/mxnet,dmlc/mxnet,jiajiechen/mxnet,larroy/mxnet,ForkedReposBak/mxnet,jamesliu/mxnet,ptrendx/mxnet,leezu/mxnet,LinkHS/incubator-mxnet,CodingCat/mxnet,navrasio/mxnet,tornadomeet/mxnet,precedenceguo/mxnet,DickJC123/mxnet,CodingCat/mxnet,dmlc/mxnet,larroy/mxnet,dmlc/mxnet,luoyetx/mxnet,szha/mxnet,luoyetx/mxnet,Northrend/mxnet,rahul003/mxnet,tornadomeet/mxnet,dmlc/mxnet,jamesliu/mxnet,Northrend/mxnet,navrasio/mxnet,ForkedReposBak/mxnet,vikingMei/mxnet,mbaijal/incubator-mxnet,apache/incubator-mxnet,tornadomeet/mxnet,eric-haibin-lin/mxnet,rahul003/mxnet,precedenceguo/mxnet,sxjscience/mxnet,vikingMei/mxnet,DickJC123/mxnet,LinkHS/incubator-mxnet,leezu/mxnet,leezu/mxnet,apache/incubator-mxnet,apache/incubator-mxnet,indhub/mxnet,larroy/mxnet,sxjscience/mxnet,vikingMei/mxnet,dmlc/mxnet,vikingMei/mxnet,fullfanta/mxnet,tlby/mxnet,ptrendx/mxnet,weleen/mxnet,LinkHS/incubator-mxnet,yajiedesign/mxnet,weleen/mxnet,vikingMei/mxnet,leezu/mxnet,DickJC123/mxnet,szha/mxnet,eric-haibin-lin/mxnet,fullfanta/mxnet,zhreshold/mxnet,jiajiechen/mxnet,zhreshold/mxnet,ptrendx/mxnet,rahul003/mxnet,dmlc/mxnet,luoyetx/mxnet,tornadomeet/mxnet,precedenceguo/mxnet,yajiedesign/mxnet,leezu/mxnet,dmlc/mxnet,jiajiechen/mxnet,CodingCat/mxnet,CodingCat/mxnet,LinkHS/incubator-mxnet,luoyetx/mxnet