tools: clarify errors when reading files

Previously certtool and ocsptool would report:
```
$ certtool --generate-request --load-privkey=foo --outfile=bar
Generating a PKCS #10 certificate request...
reading --load-privkey: foo
```

And that doesn't make apparent what the issue was. Modified
to print:
```
error reading --load-privkey: foo
```

Report and initial patch by Thibault Nélis.

Resolves !97

2 files changed, 8 insertions, 8 deletions

diff --git a/src/certtool-common.c b/src/certtool-common.c
index 60f1930ec3..99e43e5557 100644
--- a/src/certtool-common.c
+++ b/src/certtool-common.c
@@ -270,7 +270,7 @@ gnutls_privkey_t load_private_key(int mand, common_info_st * info)
 	dat.size = size;
 
 	if (!dat.data) {
-		fprintf(stderr, "reading --load-privkey: %s\n",
+		fprintf(stderr, "error reading --load-privkey: %s\n",
 			info->privkey);
 		exit(1);
 	}
@@ -313,7 +313,7 @@ load_x509_private_key(int mand, common_info_st * info)
 	dat.size = size;
 
 	if (!dat.data) {
-		fprintf(stderr, "reading --load-privkey: %s\n",
+		fprintf(stderr, "error reading --load-privkey: %s\n",
 			info->privkey);
 		exit(1);
 	}
@@ -512,7 +512,7 @@ gnutls_x509_crq_t load_request(common_info_st * info)
 	dat.size = size;
 
 	if (!dat.data) {
-		fprintf(stderr, "reading --load-request: %s\n",
+		fprintf(stderr, "error reading --load-request: %s\n",
 			info->request);
 		exit(1);
 	}
@@ -553,7 +553,7 @@ gnutls_privkey_t load_ca_private_key(common_info_st * info)
 	dat.size = size;
 
 	if (!dat.data) {
-		fprintf(stderr, "reading --load-ca-privkey: %s\n",
+		fprintf(stderr, "error reading --load-ca-privkey: %s\n",
 			info->ca_privkey);
 		exit(1);
 	}
@@ -640,7 +640,7 @@ gnutls_pubkey_t load_pubkey(int mand, common_info_st * info)
 	dat.size = size;
 
 	if (!dat.data) {
-		fprintf(stderr, "reading --load-pubkey: %s\n", info->pubkey);
+		fprintf(stderr, "error reading --load-pubkey: %s\n", info->pubkey);
 		exit(1);
 	}
 
diff --git a/src/ocsptool.c b/src/ocsptool.c
index c7610e9a5c..2aa01dde18 100644
--- a/src/ocsptool.c
+++ b/src/ocsptool.c
@@ -224,7 +224,7 @@ static gnutls_x509_crt_t load_signer(void)
 	dat.size = size;
 
 	if (!dat.data) {
-		fprintf(stderr, "reading --load-signer: %s\n",
+		fprintf(stderr, "error reading --load-signer: %s\n",
 			OPT_ARG(LOAD_SIGNER));
 		exit(1);
 	}
@@ -262,7 +262,7 @@ static gnutls_x509_crt_t load_cert(void)
 	dat.size = size;
 
 	if (!dat.data) {
-		fprintf(stderr, "reading --load-cert: %s\n",
+		fprintf(stderr, "error reading --load-cert: %s\n",
 			OPT_ARG(LOAD_CERT));
 		exit(1);
 	}
@@ -345,7 +345,7 @@ static int _verify_response(gnutls_datum_t * data, gnutls_datum_t * nonce,
 		dat.data =
 		    (void *) read_binary_file(OPT_ARG(LOAD_TRUST), &size);
 		if (dat.data == NULL) {
-			fprintf(stderr, "reading --load-trust: %s\n",
+			fprintf(stderr, "error reading --load-trust: %s\n",
 				OPT_ARG(LOAD_TRUST));
 			exit(1);
 		}