Allow skip the database server installation

This patch allows to skip the installation
of the database backend packages (MySQL or Postgres)
with the introduction of the INSTALL_DATABASE_SERVER_PACKAGES
variable (defaulted to True).
This is useful in such environments that do not require
to install the MySQL/Postgres server packages directly but using
a container serving that purpose, for those cases all the
remaining steps should be executed just skipping the
packages install.

Change-Id: I26628a31fdda3ce95ed04a2b7ae7b132c288581f
diff --git a/lib/databases/postgresql b/lib/databases/postgresql
index 1f347f5..4f0a5a0 100644
--- a/lib/databases/postgresql
+++ b/lib/databases/postgresql
@@ -13,7 +13,7 @@
 
 
 MAX_DB_CONNECTIONS=${MAX_DB_CONNECTIONS:-200}
-
+INSTALL_DATABASE_SERVER_PACKAGES=$(trueorfalse True INSTALL_DATABASE_SERVER_PACKAGES)
 
 register_database postgresql
 
@@ -104,15 +104,17 @@
     else
         sed -i "s/:root:\w\+/:root:$DATABASE_PASSWORD/" $pgpass
     fi
-    if is_ubuntu; then
-        install_package postgresql
-    elif is_fedora || is_suse; then
-        install_package postgresql-server
-        if is_fedora; then
-            sudo systemctl enable postgresql
+    if [[ "$INSTALL_DATABASE_SERVER_PACKAGES" == "True" ]]; then
+        if is_ubuntu; then
+            install_package postgresql
+        elif is_fedora || is_suse; then
+            install_package postgresql-server
+            if is_fedora; then
+                sudo systemctl enable postgresql
+            fi
+        else
+            exit_distro_not_supported "postgresql installation"
         fi
-    else
-        exit_distro_not_supported "postgresql installation"
     fi
 }