Gitlab ubuntu install script: use openssl instead makepasswd

[caruccio]

May I suggest you to use openssl, a default installed command, instead makepasswd, which must be installed yet?

$ openssl rand -base64 16
zB5HFNcYHPs2DYWt4Bsdzw==

[axilleas]

HI @caruccio you have a valid point. You can point that to the current script that will be merged into master and most likely will be the default one.