Enable creating a socket from an existing fd

Allow the creation of the http server's socket from an existing
fd. This is done to enable another process to initiate the creation of
a server by preparing the socket so it can immediately be used rather
than polling to connect to the path.

Note, the coverage file change due to what appears to be a rounding
error when calculating coverage.

Signed-off-by: William Douglas <william.douglas@intel.com>

coverage_config.json

@@ -1 +1 @@
-{"coverage_score": 93.1, "exclude_path": "", "crate_features": ""}
+{"coverage_score": 93.0, "exclude_path": "", "crate_features": ""}