HPCC-10888 Fix Potential buffer overruns

Previous code was copying password to a local buffer which went out of scope
when returning from the constructor. This change copyies the password to
a StringBuffer member where it will persist the lifetime of the object

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>
Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>
Merge pull request #5437 from RussWhitehead/pwdBuff

HPCC-10888 Fix Potential buffer overruns

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>