Fix in-source builds

The internal header directory conflicted with in-source builds causing a
build failure. This is fixed by renaming the internal header directory to
something other than maxscale.

The renaming pointed out a few problems in a couple of source files that
appeared to include internal headers when the headers were in fact public
headers.

Fixed maxctrl in-source builds by making the copying of the sources
optional.

server/core/internal/externcmd.h

@@ -0,0 +1,99 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cdefs.h>
+
+#include <unistd.h>
+
+MXS_BEGIN_DECLS
+
+#define MAXSCALE_EXTCMD_ARG_MAX 256
+
+typedef struct extern_cmd_t
+{
+    char** argv;      /**< Argument vector for the command, first being the
+                       * actual command being executed */
+    int n_exec;       /**< Number of times executed */
+    pid_t child;      /**< PID of the child process */
+    uint32_t timeout; /**< Command timeout in seconds */
+} EXTERNCMD;
+
+char* externcmd_extract_command(const char* argstr);
+
+/**
+ * Allocate a new external command.
+ *
+ * The name and parameters are copied into the external command structure so
+ * the original memory can be freed if needed.
+ *
+ * @param command Command to execute with the parameters
+ * @param timeout Command timeout in seconds
+ *
+ * @return Pointer to new external command struct or NULL if an error occurred
+ */
+EXTERNCMD* externcmd_allocate(const char* argstr, uint32_t timeout);
+
+
+/**
+ * Free a previously allocated external command
+ *
+ * @param cmd Command to free
+ */
+void externcmd_free(EXTERNCMD* cmd);
+
+/**
+ * Execute a command
+ *
+ * The output of the command must be freed by the caller by calling MXS_FREE.
+ *
+ * @param cmd  Command to execute
+ *
+ * @return The return value of the executed command or -1 on error
+ */
+int externcmd_execute(EXTERNCMD* cmd);
+
+/**
+ * Substitute all occurrences of @c match with @c replace in the arguments for @c cmd
+ *
+ * @param cmd External command
+ * @param match Match string
+ * @param replace Replacement string
+ *
+ * @return True if replacement was successful, false on error
+ */
+bool externcmd_substitute_arg(EXTERNCMD* cmd, const char* re, const char* replace);
+
+/**
+ * Check if a command can be executed
+ *
+ * Checks if the file being executed exists and if the current user has execution
+ * permissions on the file.
+ *
+ * @param argstr Command to check, can contain arguments for the command
+ *
+ * @return True if the file was found and the use has execution permissions to it
+ */
+bool externcmd_can_execute(const char* argstr);
+
+/**
+ * Simple matching of string and command
+ *
+ * @param cmd Command where the match is searched from
+ * @param match String to search for
+ *
+ * @return True if the string matched
+ */
+bool externcmd_matches(const EXTERNCMD* cmd, const char* match);
+
+MXS_END_DECLS