* add a default config (jenkinsfar.default.config.JENKINSFARM_CONFIG)
* add --time-summary option (displaying execution time is optional)
* directory-isolate tests in test_jenkins.py
* drop catching socket.error/errno.ECONNRESET in wait_jenkins_up
* check_running() only false when errno.ESRCH (other exceptions not catched)

Intermittent test failures when running successive (start|stop)'s of the same
project: wait_jenkins_(up|down) get a ECONNRESET (obviously Jenkins dying
prematurely), resulting in waiting for a dead Jenkins. This is more frequent
when the load is high.

This is not due to a specific Jenkins version, nor to starting an instance
before the previous one has finished, nor to directory issues. The cause
remains unknown.

TEST_FULL=1 python ./jenkinsfarm/test/test_jenkins.py -v \
TestJenkins.test_create TestJenkins.test_create_exisiting \
TestJenkins.test_create_fail \
TestJenkins.test_create_start_stop_destroy_force_for_real \
TestJenkins.test_create_start_stop_destroy_gracefully_for_real