Add Nexus artifact deployment initialization keyword

Add Nexus artifact deployment initialization keyword

Currently this Nexus artifact deployment initialization
keyword contains the code to connect to the tools system,
which was extracted into a keyword in SSHKeywords. This
artifact deployment initialization keyword is then called
in all suites that need to deploy test tools so any code
that explicitly opens this connection was removed from the
suites that need the Nexus artifact deployment facility.

For Netconf test suite this setup keyowrd gets called
automatically from NetconfKeywords setup keyword so
no explicit Nexus keywords initialization is done there.

This is a part of working around the bug 5206.

Change-Id: If46823d7aba92657b99d050e3098ec7c99895824
Signed-off-by: Jozef Behran <jbehran@cisco.com>