Update DeployStagedMojo.java

While deploy mojo will take into consideration the skipStaging flag, deploy staged mojo does not yet.
We have an usecase where at some point in the delivery process we need to upload (deploy) the artifacts of an already deployed maven multi module project once again to another nexus repo. We use the already existent local directory structure from the first (deferred) deploy.
I have successfully tested this change on base of the 1.6.2 version of the nexus maven staging plugin.  
basti
Multiple fixes:

NEXUS-6836: Bump XStream to fix it on java8
NEXUS-6728: Use updated zapper for preemptive auth
Bumped deps
NEXUS-6845: log the content url at info of created staging repositories
Fixing licence header

(this is unchanged file in this PR, but due to
POM parent update it's catched now)
Update SISU, align with ant tasks
Merge pull request #73 from sonatype/xstream-zapper-and-updates

Multiple fixes: XStream on Java8, zapper...
Merge pull request #74 from sonatype/NEXUS-6845-print-url-of-created-staging-repos

REVIEW: NEXUS-6845 log the content url at info of created staging repositories
Merge pull request #72 from lbastil/patch-1

Update DeployStagedMojo.java
Merge remote-tracking branch 'origin/master' into lightweight-staging