bootstrap-install: Fix agent install failure on "Linux Educacional" system

The argument "-r" used by groupadd(8) and useradd(8) is not present on
passwd package installed on "Linux Educational" distribution. Also, this
argument is not necessary in any other linux distributions, so it is being
removed.

Signed-off-by: Diego Giovane Pasqualin <dgp06@c3sl.ufpr.br>