(FACT-1317) Fix string values that look like booleans

[MikaelSmith]

YAML will read boolean strings as boolean types. When the schema states
the Fact type is a string, we should ensure it's read as a string by
YAML parsers. Quote any boolean literal representation in a
string_value.

Also fix a prior mistake in the verify_facts acceptance test, which no
longer needs to check for boolean classes for a string.

[joshcooper]

Looks like travis is complaining about trailing white space:

/home/travis/build/puppetlabs/facter/lib/src/util/string.cc:124:  Line ends in whitespace.  Consider deleting these extra spaces.  [whitespace/end_of_line] [4]

[joshcooper]

For ruby 2.1.5p273, YAML.load doesn't parse single character y|n as boolean. I don't know if that we care or if it depends on a particular yaml version.

irb(main):012:0> inputs = "y|Y|yes|Yes|YES|n|N|no|No|NO|true|True|TRUE|false|False|FALSE|on|On|ON|off|Off|OFF".split('|')
=> ["y", "Y", "yes", "Yes", "YES", "n", "N", "no", "No", "NO", "true", "True", "TRUE", "false", "False", "FALSE", "on", "On", "ON", "off", "Off", "OFF"]
irb(main):013:0> outputs = inputs.select {|value| YAML.load(value).is_a?(TrueClass) }
=> ["yes", "Yes", "YES", "true", "True", "TRUE", "on", "On", "ON"]
irb(main):014:0> inputs - outputs
=> ["y", "Y", "n", "N", "no", "No", "NO", "false", "False", "FALSE", "off", "Off", "OFF"]

[MikaelSmith]

Overquoting shouldn't be an issue, I just tried to avoid doing it in some legacy cases (like ipv4 addresses). Pushed a fix for the whitespace.

[johnduarte]

@MikaelSmith does this need to get merged into stable as well?

[MikaelSmith]

oh oops, yes. I'll cherry-pick up.