(QENG-5156) Provide Important Env Vars Set in Debug Output

This provides the Environment Variables that are pertinent to running
Beaker as an error message after a failed run or as a debug message
on a successful run in the debug log level.
Improve documentation and readability of environment parsing improvements
Ensure IS_PE only respects different values

Previously if we set the IS_PE or BEAKER_IS_PE environment variable at
all we would automatically make the run a PE run. This caused
non-obvious behavior for users that set IS_PE=false.

This changes the searching of the environment to only set the :type
option if [BEAKER_]IS_PE=yes|true.

Signed-off-by: Justin Stoller <justin@puppetlabs.com>
Clean up and document reproduction info methods in Beaker::CLI
Merge pull request #248 from justinstoller/feature/master/QENG-515-debug_env_vars

(QENG-515) Provide Important Env Vars Set in Debug Output