Create a unique machine name

Create a unique machine name

Using containers, we need a unique --file-prefix parameter in the EAL
DPDK configuration. The file-prefix name is the name of the PROX
machine. This is defined by the name parameter in the rapid.env file.
When the name parameter is not specified in the rapid.env file, the name
will be defined in the test file.
The machine name will still be defined in the same way, but when a name
is not unique, an number will be appended to the name to make it unique.

Signed-off-by: Luc Provoost <luc.provoost@gmail.com>
Change-Id: I0b4e3be60f8ddef6c7eb30bca25c041ea270e238