Fix rspec testing outside of the Openstack CI.
Fix rspec testing outside of the Openstack CI.

When testing rspec locally the r10k binary is never found because the
GEM_BIN_DIR is wrongly set to GEM_HOME/bin.  GEM_HOME is set by bundler
and GEM_HOME/bin do not point where bundler put the binary.  The
binaries are handled by bundler by changing the PATH.  rbenv, use
similar tricks.

install_all is only used outside of the CI, so this modification
wouldn't change anything as far as the official CI is concerned.

Change-Id: I07668d64f9adf6713f5c267cf45650ba92ee0b9c
Closes-Bug: 1550331

openstack/puppet-openstack-integration,openstack/puppet-openstack-integration,openstack/puppet-openstack-integration