Provide a group-name filter to get_all_security_groups() call.

This uses a helper method provided by starcluster instead of directly
calling the boto method.
Merge pull request #401 from mindprince/minor-improvement

Provide a group-name filter to get_all_security_groups() call.
add support for t2 instance types
Merge pull request #407 from rayrayson/develop

add support for t2 instance types
sshutils: pass socket timeout down to SCPClient
tests: fix for latest changes to pytest_cov

It seems with the latest changes to pytest_cov it's now impossible to
configure the coverage plugin exclusively from conftest.py without
manually loading and configuring the plugin in pytest_configure. Without
this the coverage plugin can ONLY be loaded/configured via the command
line arguments to pytest (which sucks btw). This change to pytest_cov
broke the build on travis-ci - this hack should fix that.
Merge remote-tracking branch 'trunk/develop' into vanilla_improvements