AUTO-563: personality schema validation

added schema to validate personality in launch configuration. Added
related tests
AUTO-563 validating personality in worker

Validating personality by checking base64 encoding of contents while
parallely getting limits. If we get limits, we also check content and
number of files against the limit. If not, skip limits validation
Checking invalid base64 chars - thanks @cyli
Reducing prop_value str while logging - per @cyli

+ lint fix
s/reduce/shorten - thanks @cyli
try/except inside loop

to make scope more obvious. Also renamed file to _file to avoid conflict
with builtin functions
Logging msg using PEP3103 formatter
typo fix
Merge pull request #409 from rackerlabs/auto-563-validate-personality

AUTO-563 validate personality