Remove unnecessary returns

* remove duplicated xtrace
* remove some unnecessary return

Change-Id: If9e0a979e0bd5a334e82d42572ac0b149de341d7

functions

@@ -73,7 +73,6 @@ function die_if_not_set() {
         set +o xtrace
         local evar=$1; shift
         if ! is_set $evar || [ $exitcode != 0 ]; then
-            set +o xtrace
             echo $@
             exit -1
         fi
@@ -650,10 +649,8 @@ function is_package_installed() {
 
     if [[ "$os_PACKAGE" = "deb" ]]; then
         dpkg -l "$@" > /dev/null
-        return $?
     elif [[ "$os_PACKAGE" = "rpm" ]]; then
         rpm --quiet -q "$@"
-        return $?
     else
         exit_distro_not_supported "finding if a package is installed"
     fi
@@ -664,10 +661,7 @@ function is_package_installed() {
 # is_set env-var
 function is_set() {
     local var=\$"$1"
-    if eval "[ -z \"$var\" ]"; then
-        return 1
-    fi
-    return 0
+    eval "[ -n \"$var\" ]" # For ex.: sh -c "[ -n \"$var\" ]" would be better, but several exercises depends on this
 }
 
 
@@ -973,11 +967,9 @@ function use_database {
     if [[ -z "$DATABASE_BACKENDS" ]]; then
         # The backends haven't initialized yet, just save the selection for now
         DATABASE_TYPE=$1
-        return
+    else
+        use_exclusive_service DATABASE_BACKENDS DATABASE_TYPE $1
     fi
-    use_exclusive_service DATABASE_BACKENDS DATABASE_TYPE $1 && return 0
-    ret=$?
-    return $ret
 }
 
 # Toggle enable/disable_service for services that must run exclusive of each other
@@ -1133,7 +1125,6 @@ function qpid_is_supported() {
     # Qpid was introduced to Ubuntu in precise, disallow it on oneiric; it is
     # not in openSUSE either right now.
     ( ! ([[ "$DISTRO" = "oneiric" ]] || is_suse) )
-    return $?
 }
 
 # Restore xtrace