src.ctf.fs: append error causes in ctf_fs_file_open

I hit an fopen failure in ctf_fs_file_open and noticed we were missing
some error causes for the message to be precise.  This patch adds them.

This is the result I now get when fopen fails:

    ...
    CAUSED BY [auto-disc-source-ctf-fs-37: 'source.ctf.fs'] (/home/smarchi/src/babeltrace/src/plugins/ctf/fs-src/file.c:98)
      Cannot open file: Too many open files: path=/tmp/lttng-traces/000300/mon_10.196.130.21-20180202-144403/ust/uid/0/64-bit/ch-1_4, mode=rb

Change-Id: I4dae278695b56cbedc9c7e3e5a67bc60fe6584d7
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2230
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>

src/plugins/ctf/fs-src/file.c

@@ -93,15 +93,18 @@ int ctf_fs_file_open(struct ctf_fs_file *file, const char *mode)
 	BT_COMP_LOGI("Opening file \"%s\" with mode \"%s\"", file->path->str, mode);
 	file->fp = fopen(file->path->str, mode);
 	if (!file->fp) {
-		BT_COMP_LOGE("Cannot open file \"%s\" with mode \"%s\": %s",
-			file->path->str, mode, strerror(errno));
+		BT_COMP_LOGE_APPEND_CAUSE_ERRNO(file->self_comp,
+			"Cannot open file", ": path=%s, mode=%s",
+			file->path->str, mode);
 		goto error;
 	}
 
 	BT_COMP_LOGI("Opened file: %p", file->fp);
 
 	if (fstat(fileno(file->fp), &stat)) {
-		BT_COMP_LOGE("Cannot get file information: %s", strerror(errno));
+		BT_COMP_LOGE_APPEND_CAUSE_ERRNO(file->self_comp,
+			"Cannot get file information",
+			": path=%s", file->path->str);
 		goto error;
 	}