install.sh: replaced adduser with useradd because adduser requires manual steps
install.sh: replaced adduser with useradd because adduser requires manual steps

re: ticket #7421

when running the install from the terminal (i.e. through the install link or
through devpanel.com/install.sh) adduser requests the full user information
and password to be entered manually on the terminal.

devpanel/serverlink,devpanel/serverlink,devpanel/serverlink,devpanel/serverlink,devpanel/serverlink