Without this commit airship can hang endlessly waiting for stdin
to be open. Apparently it depends on the containerd and docker
server version. This commit adds asnyc writing to stdin, this way
we don't have to wait for write to complete before starting docker
container. The code uses similar approach to upstream docker cli
implementation.
Related-To: #513
Change-Id: I2e6d4cbe37df1f8cba356af79c1c2cf18438e86c