update pre/post script to only kill process named watchman, not .*watchman.*
update pre/post script to only kill process named watchman, not .*watchman.*

Summary:
pkill -9 watchman would kill any processes that has watchman in it named.
when using alien to convert the rpm created by `arc package`, scripts called
fb-watchman.prerm and fb-watchman.postinst are ran and would kill themselves
preventing the install to succeed

Test Plan:
$ pgrep watchman
22989
┌─[09:55:07]──[chantra]──[dev421]:~/fbcode $
└──(master) >>
$ pkill -9 -x watchman || /bin/true
┌─[09:55:10]──[chantra]──[dev421]:~/fbcode $
└──(master) >>
$ pgrep watchman
┌─[09:55:12]──[chantra]──[dev421]:~/fbcode $
└──[Exit 1] (master) >>
$ pgrep watchman
28386
...
...
$ pgrep watchman
28386
┌─[09:59:13]──[chantra]──[dev421]:~/fbcode $
└──(master) >>
$ pkill -x watchman || /bin/true
┌─[09:59:19]──[chantra]──[dev421]:~/fbcode $
└──(master) >>
$ pgrep watchman
┌─[09:59:21]──[chantra]──[dev421]:~/fbcode $
└──[Exit 1] (master) >>

Reviewers: wez

Reviewed By: wez

CC: royw, sid0

Differential Revision: https://phabricator.fb.com/D1254095

Task ID: 4049275

facebook/watchman,kevinsawicki/watchman,montogeek/watchman,nodakai/watchman,Ziriax/watchman,windofthesky/watchman,supriyantomaftuh/watchman,montogeek/watchman,bhamiltoncx/watchman,hanhailong/watchman,masoncloud/watchman,nodakai/watchman,kwlzn/watchman,kevinsawicki/watchman,masoncloud/watchman,bhamiltoncx/watchman,Jonekee/watchman,wez/watchman,dcolascione/laptop-watchman,michalliu/watchman,dcolascione/laptop-watchman,besarthoxhaj/watchman,nodakai/watchman,Jonekee/watchman,bitemyapp/watchman,masoncloud/watchman,kwlzn/watchman,hanhailong/watchman,besarthoxhaj/watchman,bitemyapp/watchman,michalliu/watchman,nodakai/watchman,yun63/watchman,michalliu/watchman,sdgdsffdsfff/watchman,phmx/watchman,yonglehou/watchman,twitter/watchman,besarthoxhaj/watchman,alanwill/watchman,phmx/watchman,kwlzn/watchman,yun63/watchman,exponentjs/watchman,exponentjs/watchman,sdgdsffdsfff/watchman,michalliu/watchman,dhruvsinghal/watchman,supriyantomaftuh/watchman,phmx/watchman,kwlzn/watchman,Jonekee/watchman,Jonekee/watchman,hanhailong/watchman,hanhailong/watchman,bitemyapp/watchman,alanwill/watchman,kwlzn/watchman,facebook/watchman,yangeagle/watchman,dcolascione/laptop-watchman,yun63/watchman,Jonekee/watchman,sdgdsffdsfff/watchman,montogeek/watchman,besarthoxhaj/watchman,hanhailong/watchman,kevinsawicki/watchman,facebook/watchman,michalliu/watchman,supriyantomaftuh/watchman,Ziriax/watchman,yangeagle/watchman,yangeagle/watchman,montogeek/watchman,hanhailong/watchman,alanwill/watchman,amasad/watchman,michalliu/watchman,webmasteraxe/watchman,yangeagle/watchman,phmx/watchman,dhruvsinghal/watchman,amasad/watchman,hanhailong/watchman,twitter/watchman,nodakai/watchman,webmasteraxe/watchman,yun63/watchman,yonglehou/watchman,yun63/watchman,wez/watchman,twitter/watchman,dcolascione/laptop-watchman,yangeagle/watchman,dhruvsinghal/watchman,masoncloud/watchman,montogeek/watchman,twitter/watchman,dcolascione/laptop-watchman,amasad/watchman,masoncloud/watchman,nodakai/watchman,sdgdsffdsfff/watchman,bitemyapp/watchman,amasad/watchman,yonglehou/watchman,wez/watchman,bitemyapp/watchman,yonglehou/watchman,sdgdsffdsfff/watchman,facebook/watchman,windofthesky/watchman,exponentjs/watchman,yangeagle/watchman,twitter/watchman,exponentjs/watchman,alanwill/watchman,windofthesky/watchman,wez/watchman,sdgdsffdsfff/watchman,Jonekee/watchman,wez/watchman,bhamiltoncx/watchman,besarthoxhaj/watchman,webmasteraxe/watchman,nodakai/watchman,amasad/watchman,bitemyapp/watchman,amasad/watchman,masoncloud/watchman,Ziriax/watchman,dhruvsinghal/watchman,montogeek/watchman,bhamiltoncx/watchman,kevinsawicki/watchman,hanhailong/watchman,windofthesky/watchman,wez/watchman,masoncloud/watchman,yun63/watchman,windofthesky/watchman,dhruvsinghal/watchman,yangeagle/watchman,wez/watchman,dhruvsinghal/watchman,exponentjs/watchman,phmx/watchman,Jonekee/watchman,Jonekee/watchman,yonglehou/watchman,webmasteraxe/watchman,supriyantomaftuh/watchman,dhruvsinghal/watchman,amasad/watchman,twitter/watchman,nodakai/watchman,windofthesky/watchman,facebook/watchman,kwlzn/watchman,windofthesky/watchman,supriyantomaftuh/watchman,twitter/watchman,webmasteraxe/watchman,Ziriax/watchman,Ziriax/watchman,wez/watchman,besarthoxhaj/watchman,nodakai/watchman,yonglehou/watchman,kevinsawicki/watchman,kevinsawicki/watchman,bitemyapp/watchman,alanwill/watchman,sdgdsffdsfff/watchman,facebook/watchman,bhamiltoncx/watchman,michalliu/watchman,montogeek/watchman,bitemyapp/watchman,webmasteraxe/watchman,yonglehou/watchman,dcolascione/laptop-watchman,yonglehou/watchman,kwlzn/watchman,dhruvsinghal/watchman,montogeek/watchman,michalliu/watchman,besarthoxhaj/watchman,supriyantomaftuh/watchman,facebook/watchman,bhamiltoncx/watchman,twitter/watchman,amasad/watchman,webmasteraxe/watchman,masoncloud/watchman,supriyantomaftuh/watchman,alanwill/watchman,wez/watchman,besarthoxhaj/watchman,sdgdsffdsfff/watchman,Ziriax/watchman,supriyantomaftuh/watchman,dcolascione/laptop-watchman,yun63/watchman,phmx/watchman,webmasteraxe/watchman,facebook/watchman,facebook/watchman,exponentjs/watchman,kevinsawicki/watchman,yun63/watchman,dcolascione/laptop-watchman