Set timeout multiplier to 10 for acceptance tests run by Drone

Sometimes, acceptance tests run by Drone fail due to a timeout when
starting the web browser sessions. Increasing the timeout should
minimize the possibility of the failure happening, although it can not
guarantee that it will not happen. A timeout multiplier of 10 was set
just because it looks like a reasonable margin of time, although it is
not based on any hard data.

The timeout multiplier affects too the timeout used when finding
elements. Like when starting a session, increasing the find timeout
simply gives the acceptance tests more time to find the objects before
giving up, so it does not change their behaviour when successful and can
also prevent failures due to default timeouts being too low for a
strained system.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>