Make GCE image search list comma separated

This updates the option for the image search project list to use commas (,)
rather than colons (:) to separate entries -- group affiliated projects are
identified with a colon in the GCE system, making them impossible to use in
the previous mode.

This also follows the convention of the upstream gcutil CLI.

Signed-off-by: Daniel Pittman <daniel@rimspace.net>
Merge pull request #122 from daniel-pittman/gce-avoid-colon-in-project-list

Make GCE image search list comma separated
Merge pull request #123 from daniel-pittman/gce-support-google-compute-ssh-key-too

Support `google_compute_engine` ssh key by default
(packaging) Update CHANGELOG, Modulefile for 1.1.1
Expand tildes in key path before testing for existence

Unfortunately, while Ruby will implicitly expand a tilde in a file path in
most places, it doesn't actually do that for file existence tests.

This manually expands the path before performing the test, which makes the key
default detection actually work as expected.

Signed-off-by: Daniel Pittman <daniel@rimspace.net>