Correct a minor error in gpMgmt Makefile
Correct a minor error in gpMgmt Makefile

Makefiles use sh as shell by default unless ${SHELL} is set. This leads
conditionals expressed in '[[...]]' to not be portable. For example in ubuntu
the following error is emitted during install:
	/bin/sh: 1: [[: not found

Use the more portable '[...] && [...]' yet more cumbersome syntax.

xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,jmcatamney/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,jmcatamney/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,adam8157/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,adam8157/gpdb,lisakowen/gpdb,jmcatamney/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,xinzweb/gpdb,50wu/gpdb,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,adam8157/gpdb,xinzweb/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,xinzweb/gpdb,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb,adam8157/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,greenplum-db/gpdb