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/mysql b/lib/databases/mysql
index 8edbf8c..30e4b7c 100644
--- a/lib/databases/mysql
+++ b/lib/databases/mysql
@@ -12,6 +12,7 @@
 set +o xtrace
 
 MYSQL_DRIVER=${MYSQL_DRIVER:-PyMySQL}
+INSTALL_DATABASE_SERVER_PACKAGES=$(trueorfalse True INSTALL_DATABASE_SERVER_PACKAGES)
 
 register_database mysql
 
@@ -175,18 +176,20 @@
         chmod 0600 $HOME/.my.cnf
     fi
     # Install mysql-server
-    if is_oraclelinux; then
-        install_package mysql-community-server
-    elif is_fedora; then
-        install_package mariadb-server mariadb-devel mariadb
-        sudo systemctl enable $MYSQL_SERVICE_NAME
-    elif is_suse; then
-        install_package mariadb-server
-        sudo systemctl enable $MYSQL_SERVICE_NAME
-    elif is_ubuntu; then
-        install_package $MYSQL_SERVICE_NAME-server
-    else
-        exit_distro_not_supported "mysql installation"
+    if [[ "$INSTALL_DATABASE_SERVER_PACKAGES" == "True" ]]; then
+        if is_oraclelinux; then
+            install_package mysql-community-server
+        elif is_fedora; then
+            install_package mariadb-server mariadb-devel mariadb
+            sudo systemctl enable $MYSQL_SERVICE_NAME
+        elif is_suse; then
+            install_package mariadb-server
+            sudo systemctl enable $MYSQL_SERVICE_NAME
+        elif is_ubuntu; then
+            install_package $MYSQL_SERVICE_NAME-server
+        else
+            exit_distro_not_supported "mysql installation"
+        fi
     fi
 }