reduce logging from failed decryption with decrypt=lax
do not bruteforce Properties decrypts with unknown passphrase

this greatly decreases startup time with lots of data encrypted with
missing passphrases
Default to only (En|De)crypt vars that need it

For both Encrypting and Decrypting of Properties
files, we should by default only attempt to execute
on elements that have an "encrypted" attribute defined.

The code will already attempt to encrypt every element
if nothing in the current document matches this xpath,
which catches the case of a user trying to fully
encrypt a completely new properties file.

Conflicts:
	src/lib/Bcfg2/Server/Encryption.py
fixed pylint/pep-8 tests
testsuite: more unit test fixes