This commit adds a test to ensure that settings for a theme are retained
even if saving a theme setting after a theme setting migration fails.
Prior to the fix introduced in 35bc27a36d,
failing to save the new settings will actually cause some or all of the
theme's setting to be lost.
This commit fixes a bug in the `themes:update` rake task which resulted
in the ActiveRecord transaction not being rolled back when an error was
encountered. The transaction was first introduced in
7f0682f4f2 which changed a `begin..rescue`
block to `transaction do..rescue`. The problem with that change
prevented the transaction from ever rolling back as the code block
looks something like this:
```
transaction do
begin
update_theme
rescue => e
# surpress error
end
end
```
From the transaction's point of view now, it will never rollback even if
an error was encountered when updating the remote theme because it will
never see the error.
Instead we should have done something like this if we wanted to surpress
the errors encountered while still ensuring that the transaction is
rolled back.
```
begin
transaction do
update_theme
end
rescue => e
# surpress error
end
```
