docs: Add warnings about password selection

Some services fail when using special characters in passwords, add some
warnings to our docs.

Closes-Bug: 1744985
Change-Id: I601149e2e7362507b38f01719f7197385a27e0a8

Author: osfrickler

doc/source/configuration.rst

@@ -181,6 +181,9 @@ values that most often need to be set.
 If the ``*_PASSWORD`` variables are not set here you will be prompted to
 enter values for them by ``stack.sh``.
 
+.. warning:: Only use alphanumeric characters in your passwords, as some
+   services fail to work when using special characters.
+
 The network ranges must not overlap with any networks in use on the
 host. Overlap is not uncommon as RFC-1918 'private' ranges are commonly
 used for both the local networking and Nova's fixed and floating ranges.

doc/source/guides/single-machine.rst

@@ -106,6 +106,9 @@ do the following:
 -  Set the service password. This is used by the OpenStack services
    (Nova, Glance, etc) to authenticate with Keystone.
 
+.. warning:: Only use alphanumeric characters in your passwords, as some
+   services fail to work when using special characters.
+
 ``local.conf`` should look something like this:
 
 .. code-block:: ini

doc/source/index.rst

@@ -101,7 +101,10 @@ devstack git repo.
 This is the minimum required config to get started with DevStack.
 
 .. note:: There is a sample :download:`local.conf </assets/local.conf>` file
-    under the *samples* directory in the devstack repository.
+   under the *samples* directory in the devstack repository.
+
+.. warning:: Only use alphanumeric characters in your passwords, as some
+   services fail to work when using special characters.
 
 Start the install
 -----------------