turn apply spec network configuration in a fixed struct

Signed-off-by: John Foley <jfoley@pivotallabs.com>
made customNetwork a private struct

Signed-off-by: John Foley <jfoley@pivotallabs.com>
rename errChan to errCh

Signed-off-by: John Foley <jfoley@pivotallabs.com>
added default network resolver
allow to pass in non-string options to blobstores

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>
clean up external blobstore test

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>