Jenkins is trying to deploy a new JDK onto a slave and is using a GNU-extension to tar which gunzips tarfiles on the fly:

Building remotely on despina in workspace /export/home/hudson/workspace/xunit
Installing JDK jdk-7-oth-JPR
Downloading JDK from http://download.oracle.com/otn-pub/java/jdk/7/jdk-7-solaris-sparcv9.tar.gz
Downloading 12979380bytes
Installing /export/home/hudson/tools/JRE/jdk.sh
[JRE] $ tar xvzf /export/home/hudson/tools/JRE/jdk.sh
tar: z: unknown function modifier
Usage: tar

{c|r|t|u|x}

[BDeEFhilmnopPqTvw@[0-7]][bfk][X...] [blocksize] [tarfile] [size] [exclude-file...]

{file | -I include-file | -C directory file}

...
ERROR: Failed to install JDK. Exit code=1
Finished: FAILURE

The correct way to unpack this tarfile for Solaris (or any POSIX machine) is "gunzip -c /export/home/hudson/tools/JRE/jdk.sh | tar -xvf -"