Spectrum NCM configuration comparison mask improvement

Idea created by mwegner on Aug 16, 2016

    Currently, NCM does line by line masking of the diffs.  This is usually sufficient, but sometimes context is needed in the comparison masks.  For example, Fortigate appliances fill in unconfigured private key or cert fields with garbage values.  It would be nice if configuration comparison were expanded to allow comparison mask regexps to 1) make multi-line matches and 2) mask against the entire configuration.