bootstrap-install: Changed installer to remove old seed_mec sudoers(1) rule

Instead of doing nothing, remove the old rule and add the new one to
sudoers(1) file.

This modification corrects an error which the previous agent version caused
in outdated systems (e.g. LE 3, Ubuntu 8), making the sudoers(1) file
unreadable.

Signed-off-by: Erik Alexandre Pucci <eap08@c3sl.ufpr.br>
Acked-by: Adriano da Luz <al08@c3sl.ufpr.br>
Acked-by: Bruno Ribas <ribas@c3sl.ufpr.br>

bootstraps/bootstrap-install

@@ -193,8 +193,13 @@ crontab -u seed_mec -r
 if ! test -n "${PROJECTOR}" -o -f "/usr/sbin/projetor" -o \
           -f "/etc/cmpc-release" -o -n "${UCA_SERVER}" -o \
           -n "${UCA_CLASSMATE}"; then
+    # Remove any possible line containing a rule for seed_mec user before adding
+    # root permissions in the sudoers file
+    TMPFILE=$(mktemp)
+    sed '/^seed_mec[\t ]*ALL=(ALL/d' /etc/sudoers > "${TMPFILE}"
+    mv "${TMPFILE}" /etc/sudoers
+    chmod 440 /etc/sudoers
     # Add root permissions to seed_mec user, without the need of password
-    if ! grep -q "seed_mec" /etc/sudoers; then
     if ! $(echo -e "seed_mec\tALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers)
     then
         printf "ERRO: Falha ao adicionar permissões de super-usuário %b" \
@@ -202,7 +207,6 @@ if ! test -n "${PROJECTOR}" -o -f "/usr/sbin/projetor" -o \
         exit 3
     fi
 fi
-fi
 
 # Uncompress tar package and check its integrity
 tail -n +${BOOTSTRAP_LINES} $0 > "${SEED_MEC_HOME}/${FILE}"