unpin rbvmomi from 1.6.0

- rbvmomi issue fixed for ruby 1.8.7, should be good to go now
pin rubygems to 2.2.1 for travis CI

- issue with 1.8.7 bustage fixed in rubygems 2.2.1
http://blog.rubygems.org/2014/01/06/2.2.1-released.html
(QA-753) Don't write or read the PE tarball more than we have to

The PE tarball is big and our storage isn't always happy about
that. By streaming the tarball unpack, we can avoid a write and then a
read of the 800MB tar. On a matrix of 200 nodes, that comes up to 20
million 4K blocks written then read, for no real gain.
Merge pull request #115 from branan/pe_tgz_unpack

(QA-753) Don't write or read the PE tarball more than we have to
Merge pull request #103 from anodelman/pin-rbvmomi

unpin rbvmomi from 1.6.0
Merge pull request #104 from anodelman/pin-rubygems

unpin rubygems for travis CI