Improved platform support.

Improved the detection of a valid GDB server where we actually can connect to a socket, but then it doesn't read or write anything (which happens with some USB mux software).

Host::MakeDirectory() now can make as many intermediate directories as needed.

The testsuite now has very initial support for remote test suite running. When running on a remote platform, the setUp function for the test will make a new directory and select it as the working directory on the remote host.

Added a common function that can be used to create the short option string for getopt_long calls.