Adds funcs to return strings w/ prefixes and suffixes

[nkinkade]

Previously, the only string function returned a typical mlab hostname. This commit adds additional string functions to return various combinations of the hostname with or without prefixes and suffixes.

Additionally, this commit modifies the v2 regexp to capture and return any prefix. Previously the prefix match was a non-capturing group.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 1225

• 25 of 25 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 94.469%

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Totals
Change from base Build 1214:	0.03%
Covered Lines:	2169
Relevant Lines:	2296

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💛 - Coveralls