Dedicated exception for PR malformed requirements

Create dedicated manager exception MalformedRequirements returns
HTTP 400 Malformed requirements %(rqrms)s
when the requirements of reservation are malformed

Added small bugfix allow to create reservation
with one character value of propety

Closes-Bug: #1305048
Change-Id: I5e5fa012dd9556182eac8def0124fa683f9b677c