KUDU-1251 Some build dependencies missing from README
KUDU-1251 Some build dependencies missing from README

Also added the convenience Bash script for OSX to mirror
what RHEL and Ubuntu have, and corrected a mention of
CentOS in the Ubuntu section.

Change-Id: I11c0fd68a6bb2eb905d311b03db65a36ed190bd2
Reviewed-on: http://gerrit.cloudera.org:8080/1547
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@cloudera.com>
Reviewed-by: Misty Stanley-Jones <b9f9ef9e00c258208ea831c64cc129eda4ac78b4@apache.org>
Tested-by: Misty Stanley-Jones <b9f9ef9e00c258208ea831c64cc129eda4ac78b4@apache.org>

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