Add support for the `test_timeout_factor' global variable letting a test
case scale the wait timeout used for code execution. This is useful for
particularly slow test cases for which increasing the wait timeout
globally would be excessive.
* baseboards/qemu.exp (qemu_load): Handle `test_timeout_factor'.
* config/gdb-comm.exp (gdb_comm_load): Likewise.
* config/gdb_stub.exp (gdb_stub_load): Likewise.
* config/sim.exp (sim_load): Likewise.
* config/unix.exp (unix_load): Likewise.
* doc/dejagnu.texi (Local configuration file): Document
`test_timeout_factor'.