For a local process based executor usage currently to ensure
that task emitted notifications are proxied we use the multi
processing library and use its queue concept. This sadly creates
a proxy process that gets associated, and this proxy process
handles the queue and messages sent to and from it. Instead of
doing this we can instead just create a temporary local socket
using a random socket and have tasks (which are running in
different processes) use that to communicate back any emitted
notifications instead (and we can use the asyncore module to handle
the emitted notifications since it handles the lower level socket
reading, polling and dispatching).

To ensure that the socket created is somewhat secure we use a
similar process as the multi-processing library uses where we
sign all messages with a hmac that uses a one time key that only
the main process and the child process know about (and reject
any messages that do not validate using this key).

Change-Id: Iff9180054bf14495e5667af00ae2fafbdbc23791

Change-Id: Id9adbc50bd51adc77ce88f698ad0ea2ee63fc5e2

Under some cirumstances it is ok to recompute
a value when raced to by multiple threads, for these
cases allow the cachedproperty to avoid needing and
using a lock.

Change-Id: Icb71cb5ea280185cfb120671be900435dabcd50b

Christmas came early.

Closes-Bug: #1479466

Change-Id: I931d826690c925f022dbfffe9afb7bf41345b1d0

Instead of a custom loop and backoff just use the retrying
library to do this same code and delegate the loop complexity
to it instead.

Change-Id: Iaf02cc728d2a2cfc7077300e03d7ef25522717b7

Change-Id: I43465b8f5868e64bdf38d2873417a8a4a403a23b

Change-Id: I2ff3b9bb4d0b8143163e4bf370f10c74e79dbd31

Instead of having the compiler do any validation on the
graph it has created instead have the compiler just compile
and have the engine that uses that compiled result do any
post compilation validation instead.

This makes it more clear that the compiler just compiles a
flow (and tasks and nested flows) into a graph, and that is
all that it does.

Change-Id: I96a35d732dc2be9fc8bc8dc6466256a19ac2df6d