Added HADOOP_BIN & HADOOP_SBIN to PATH
Lower the acceptable count threshold in thread test to 5

The tests were sometimes failing on TravisCI (slower machines) with
counts below 100.  A test where we left the GIL locked showed that the
counter value doesn't change at all across calls, so in theory even an
increment of 1 would demonstrate that the mechanism is working.
Set the PYTHONPATH on hadoop-env.sh
Explicit PYTHONPATH in the travis environment
Fixed PATH on hadoop_env.sh
Reactived virtualenv after the python-all-dev installation
PYTHONPATH in hadoop_env.sh is equal to the travis PYTHONPATH
Fixed the syntax of the hdfs command in run_wordcount_* scripts of pydoop_submit examples