Support multiple profiles

[smcavallo]

Allow multiple profiles to exist in the softlayer credential file.
The current implementation only allows one set of creds under a key of ['softlayer']

Proposed implementation allows multiple sets of credentials in the file using an environment variable of "SL_PROFILE" to determine which set to use. This is a standard pattern with credential files and ruby sdks.
This allows credentials for multiple environments to be stored in the same file.

[coveralls]

Coverage increased (+0.004%) to 99.767% when pulling 06e2a3a on smcavallo:support_multiple_profiles into 7889052 on softlayer:master.

[coveralls]

Coverage increased (+0.004%) to 99.767% when pulling 06e2a3a on smcavallo:support_multiple_profiles into 7889052 on softlayer:master.

[smcavallo]

@SLsthompson - looking for a review and for a new version of the softlayer_api gem to be published to rubygems

[allmightyspiff]

Looks good to me. Although Piglet's api_key should be something like "Oh, d-d-d-dear!" :)