HTTP API: Pass job timeout in HTTP headers

HTTP API: Pass job timeout in HTTP headers

Users may want to check timeout value when request gets its resources
or access to worker is prolonged. Currently it can be only done with
GetRequestInfo() which returns all information about given request. To
make this action more convenient HTTP API server will set
Boruta-Job-Timeout header when request is in "IN PROGRESS" state. On the
client side GetJobTimeout is added. It should be also faster way to
obtain timeout value as HEAD method is used instead of GET and there's
no JSON parsing.

Change-Id: I9533f64be063e97b09c5e378a87968395d6b4072
Signed-off-by: Maciej Wereski <m.wereski@partner.samsung.com>