Give warning, not error, when Hadoop not found

When Trafodion has just been untarred from a product file obtained from
downloads.trafodion.org, and no Hadoop is found, give a warning instead of
an error and suggest that install_local_hadoop may be needed.

In that situation, do not put 4 colons at front of CLASSPATH.

Change-Id: If207b5999df37d3139015ff88bc4bde4686f7919
Merge "Give warning, not error, when Hadoop not found"