check and only allow to create database in a mount point

https://bugzilla.redhat.com/show_bug.cgi?id=1431815
https://bugzilla.redhat.com/show_bug.cgi?id=1425153

lib/gems/pending/appliance_console/internal_database_configuration.rb

@@ -3,6 +3,7 @@
 require "pathname"
 require "util/postgres_admin"
 require "pg"
+require "linux_admin"
 
 RAILS_ROOT ||= Pathname.new(__dir__).join("../../../")
 
@@ -67,6 +68,9 @@ def ask_questions
 
     def choose_disk
       @disk = ask_for_disk("database disk")
+      error_message = "The disk for database must be a mount point"
+      raise error_message unless disk || pg_mount_point?
+      disk
     end
 
     def initialize_postgresql_disk
@@ -108,7 +112,7 @@ def post_activation
     private
 
     def mount_point
-      Pathname.new(ENV.fetch("APPLIANCE_PG_MOUNT_POINT"))
+      PostgresAdmin.mount_point
     end
 
     def copy_template(src, src_dir = self.class.postgresql_template, dest_dir = PostgresAdmin.data_directory)
@@ -121,6 +125,10 @@ def copy_template(src, src_dir = self.class.postgresql_template, dest_dir = Post
       end
     end
 
+    def pg_mount_point?
+      LinuxAdmin::LogicalVolume.mount_point_exists?(mount_point)
+    end
+
     def run_initdb
       AwesomeSpawn.run!("service", :params => {nil => [PostgresAdmin.service_name, "initdb"]})
     end