ACCUMULO-1556 Clarify initialization error for used fs

The Initialize class now generates clearer and more informative
error messages if an initialized instance is discovered. The
messages vary depending on whether instance.dfs.uri is used. The
values of instance.dfs.uri and instance.dfs.dir are also logged.
Merge branch '1.4.5-SNAPSHOT' into 1.5.1-SNAPSHOT
ACCUMULO-1556 Clarify initialization error for used fs

The Initialize class now generates clearer and more informative
error messages if an initialized instance is discovered. The
messages vary depending on whether instance.dfs.uri is used. The
values of instance.dfs.uri and instance.dfs.dir are also logged.
Fixes "hostname -a" errors on OS X