ssh: breakout ups ssh to its own package

This was done for clearer separation of function. A subsequent update will (hopefully) make the SSL command more robust so it works for both NMC2 and NMC3.

The method for sending shell commands was also updated to use an interactive shell instead. This allows capturing responses of the commands which will be needed to deduce if devices are NMC2 or NMC3.

pkg/apcssh/shell_helpers.go

@@ -0,0 +1,38 @@
+package apcssh
+
+import (
+	"regexp"
+)
+
+// scanAPCShell is a SplitFunc to capture shell output after each interactive
+// shell command is run
+func scanAPCShell(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	if atEOF && len(data) == 0 {
+		return 0, nil, nil
+	}
+
+	// regex for shell prompt (e.g., `apc@apc>`)
+	re := regexp.MustCompile(`(\r\n|\r|\n)[A-Za-z0-0.]+@[A-Za-z0-0.]+>`)
+
+	// find match for prompt
+	if index := re.FindStringIndex(string(data)); index != nil {
+		// advance starts after the prompt; token is everything before the prompt
+		return index[1], dropCR(data[0:index[0]]), nil
+	}
+
+	// If we're at EOF, we have a final, non-terminated line. Return it.
+	if atEOF {
+		return len(data), dropCR(data), nil
+	}
+
+	// Request more data.
+	return 0, nil, nil
+}
+
+// dropCR drops a terminal \r from the data.
+func dropCR(data []byte) []byte {
+	if len(data) > 0 && data[len(data)-1] == '\r' {
+		return data[0 : len(data)-1]
+	}
+	return data
+}