(1093) - Fix unresolved fact error

(1093) - Fix unresolved fact error

Prior to this commit, work was carried out on this module to update all instances of the now deprecated Facter::Util::Resolution, and replace all with its newer and supported counterpart Facter::Core::Execution.
However, these do not behave exactly the same. Facter::Util::Resolution initially ran a which to locate the binary before executing, preventing any errors from occuring. The newer Facter::Core::Execution method did not do this, instead it attempted to execut>

This commit aims to introduce an "on_fail:false" flag to each execute statement, so that a failed execute will return false (boolean) as oppose to an error, which can then be used for further logic.