jvpp: make shm_prefix configurable (VPP-591)

jvpp: make shm_prefix configurable (VPP-591)

svm.c - set default map region root path only if root path is not
already present
memory_shared.c - added option for tests to send memory region name
and root path in one variable, if so name and root path are
separated here and set to map region structure so find function
can find it properly
jvpp-registry.c - added parameters shmPrefix to be able pass +
removed sudo restriction
specific shared memory prefix that is used while starting
python tests(see framework.py)
JVppRegistyImpl - added option to specify shmPrefix
VppJNIConnection - added option to specify shmPrefix

Change-Id: I3f89f867fb9b20eef00fbd497cb0e41b25d6eab7
Signed-off-by: Jan Srnicek <jsrnicek@cisco.com>
Signed-off-by: Matej Perina <mperina@cisco.com>