tests: Move test_infra from a module to crate

It must be specified as excluded from the workspace as it must not be
built on non-test targets due to issues with the ssh2 dependency and the
musl toolchain.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

Cargo.lock

@@ -230,7 +230,7 @@ dependencies = [
  "seccomp",
  "serde_json",
  "signal-hook",
- "ssh2",
+ "test_infra",
  "thiserror",
  "vm-memory",
  "vmm",
@@ -1098,6 +1098,18 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "test_infra"
+version = "0.1.0"
+dependencies = [
+ "dirs",
+ "epoll",
+ "libc",
+ "ssh2",
+ "vmm-sys-util",
+ "wait-timeout",
+]
+
 [[package]]
 name = "textwrap"
 version = "0.11.0"