StanbolTestBase should support HttpHeaders for parsed SERVER_READY properties

The StanbTestBase allows to parse

URI:value

pairs that are checked before Integration tests are executed.

A lot of RESTful service do also depend on HTTP headers to be set (e.g. for content negotiation). To support this the parsed of the parsed value should be extended to also support HTTP header

URI:value:

{header1}

[:

{value1}

:

{header2}

:

{value2}

: ...]

empty header/values should be ignored