GDB plugin: enables GNU Debugger features

Such as the ability to run any number of applications inside the
debugger transparently.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
job runtime: set the currently running test

So that other parts of the framework may act upon it if necessary.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
GDB: add transparent support to avocado/utils/process.py

So that any code using our process API can be run through a debugger.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
GDB: add paused and paused_msg to the test state and job main loop

paused is a boolean that indicates if the test is paused, and paused_msg
may contain a message to give to the user running the test.

Signed-off-by: Cleber Rosa <crosa@redhat.com>