[TESTAPI] Upgrade the docker without changing the python2.7 code

[TESTAPI] Upgrade the docker without changing the python2.7 code

migratio to python 3 is not a long flmeuve tranquille
some libraries used are no more maintained
this option considers updating the dockerfile without changing the
original code
it includes
- a change of the baseline image (move from 14.04 to 18.04)
- a better fix of python lib versions
- the introduction of an ubuntu user (to be better used)

Issue-ID: FUNCTEST-1026

Signed-off-by: morganrol <morgan.richomme@orange.com>
Change-Id: I37c8262d1ec20151e2402e298751ca39c36d1a7e