Fix pax exam issue

Fix pax exam issue

auto-release is all of a sudden seeing these failure for the
ToasterTest:

2018-06-17T01:54:27,557 | WARN  | pool-2-thread-1  | AetherBasedResolver              | 2 - org.ops4j.pax.url.mvn - 2.5.4 | Error resolving artifact org.ops4j.pax.tipi:org.ops4j.pax.tipi.junit:jar:4.12.0.1: [Could not find artifact org.ops4j.pax.tipi:org.ops4j.pax.tipi.junit:jar:4.12.0.1 in defaultlocal (file:/tmp/r/), Could not find artifact org.ops4j.pax.tipi:org.ops4j.pax.tipi.junit:jar:4.12.0.1 in system.repository (file:/w/workspace/autorelease-release-oxygen/controller/opendaylight/md-sal/samples/toaster-it/target/exam/f302a2c9-2cc5-40dc-8c2b-02b85c0fe216/system/)]

2018-06-17T01:54:27,557 | WARN  | pool-2-thread-3  | AetherBasedResolver              | 2 - org.ops4j.pax.url.mvn - 2.5.4 | Error resolving artifact org.ops4j.pax.tipi:org.ops4j.pax.tipi.hamcrest.core:jar:1.3.0.1: [Could not find artifact org.ops4j.pax.tipi:org.ops4j.pax.tipi.hamcrest.core:jar:1.3.0.1 in defaultlocal (file:/tmp/r/), Could not find artifact org.ops4j.pax.tipi:org.ops4j.pax.tipi.hamcrest.core:jar:1.3.0.1 in system.repository (file:/w/workspace/autorelease-release-oxygen/controller/opendaylight/md-sal/samples/toaster-it/target/exam/f302a2c9-2cc5-40dc-8c2b-02b85c0fe216/system/)]

I was able to repro locally by removing the
org.ops4j.pax.tipi.hamcrest.junit and org.ops4j.pax.tipi.hamcrest.core artifacts
from ny local .m2 repo. Adding the dependencies to the mdsal-it-base pom
causes them to be downloaded and fixes the issue. However it's a mystery why
this issue all of a sudden popped up and why it seems we have to explicitly
reference those depnedencies.

Change-Id: Ic614f243d0a79aa298961a4a340d4fa3fb483843
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>