CA-119115: Use a portable 'timeout' parameter for dhclient.

In Centos 5.7, dhclient takes -T <timeout> as an argument (see manpage).
This is a RHEL extension.

In Centos 6.4 dhclient, -T is for 'temoporary ipv6 address'.

Due to this incompatibility, upgrade from Sanibel to EA-1173exp branch
fails due to dhcp failure.

Signed-off-by: Joby Poriyath <joby.poriyath@citrix.com>