`spike secret get` returns a connection error if secret does not exist; it should display a "secret not found" message instead.

[v0lkan]

volkan@spike-fedora:~/WORKSPACE/spike$ spike secret get test
Error: failure reading secret: post: Problem connecting to peer
Usage:
  spike secret get <path> [key] [flags]

Flags:
  -f, --format string   Format to use. Valid options: plain, p, yaml, y, json, j (default "plain")
  -h, --help            help for get
  -v, --version int     Specific version to retrieve

failure reading secret: post: Problem connecting to peer
volkan@spike-fedora:~/WORKSPACE/spike$ spike secret get test -f yaml
Error: failure reading secret: post: Problem connecting to peer
Usage:
  spike secret get <path> [key] [flags]

Flags:
  -f, --format string   Format to use. Valid options: plain, p, yaml, y, json, j (default "plain")
  -h, --help            help for get
  -v, --version int     Specific version to retrieve

failure reading secret: post: Problem connecting to peer