Description of problem:

Typically scripts include a line-ending character at the end of their output.

Therefore, ProcessExecutionResults.getCapturedOutput() used by the plugin will include line end characters.

However, the option 'availabilityOutputRegex' option makes no mention that:
1) The regex must match the entire output of the command, including line end characters
2) And constructs such as .* will not match the end of line characters. 

For example, if my command outputs 'foo\n' when run, the following will not work:

      <plugin-configuration>
        <c:simple-property name="executable" required="true" default="..." />
        <c:simple-property name="availabilityOutputRegex" default="foo" />
      </plugin-configuration>

Nor will:

        <c:simple-property name="availabilityOutputRegex" default="foo.*" />

A work around is to include (?s) at the beginning

        <c:simple-property name="availabilityOutputRegex" default="(?s)foo.*" />

Suggested solutions:

1) Trim the whitespace by default from the output. This could possibly break some
existing plugin users, but highly unlikely.
2) Include Pattern.DOTALL option by default.
3) Make some note that (?s) should be included if the output contains a line break.
4) Instead of using Pattern.matcher().matches() use Pattern.matcher().find() instead.

1 or 4 is probably the most intuitive solution. Whitespace is rarely important to consider.

And just a guess, I doubt this plugin was well tested or this feature used in any case.