Debian and Ubuntu>Precise needs bundler package, not ruby-bundler

Under Debian and Ubuntu (Trusty release), ruby-bundler
package is just called bundler.
Trusty has a transitional package called ruby-bundler
but it should be better to stick to proper name.
Add a conditional to detect operating system and if it's
Precise install ruby-bundler package, it not install
bundler one.

Change-Id: Ib49f7947187f844effa49d0e7501ea37c86bde66
Merge "Debian and Ubuntu>Precise needs bundler package, not ruby-bundler"