qemu: Introduce two new job types

qemu: Introduce two new job types

Currently, all of domain "save/dump/managed save/migration"
use the same function "qemudDomainWaitForMigrationComplete"
to wait the job finished, but the error messages are all
about "migration", e.g. when a domain saving job is canceled
by user, "migration was cancled by client" will be throwed as
an error message, which will be confused for user.

As a solution, intoduce two new job types(QEMU_JOB_SAVE,
QEMU_JOB_DUMP), and set "priv->jobActive" to "QEMU_JOB_SAVE"
before saving, to "QEMU_JOB_DUMP" before dumping, so that we
could get the real job type in
"qemudDomainWaitForMigrationComplete", and give more clear
message further.

And as It's not important to figure out what's the exact job
is in the DEBUG and WARN log, also we don't need translated
string in logs, simply repace "migration" with "job" in some
statements.

* src/qemu/qemu_driver.c