The init script for the test container writes additional lines to
the .bashrc of the user. This was done via a `cat` multiline
instruction, which is implemented internally by writing a
temporary file to TMPDIR (/tmp in this case) first. Docker fails
to provide /tmp just after creation, which results in a race
condition that rarely makes the init fail. Changed the `cat`
statement to multiple `echo`s.
Co-authored-by: Matt Clay <matt@mystile.com>
