REGTESTS: relax strerror matching to avoid a failure on libmusl

The regtest4be_1srv_smtpchk_httpchk_layer47errors.vtc fails on musl
because it reports "Network unreachable" for -EUNREACH while the
check matches "Network is unreachable" as on other OSes. Let's just
replace " is" with ".*". It now works on both glibc and musl.

Author: wtarreau

reg-tests/checks/4be_1srv_smtpchk_httpchk_layer47errors.vtc

@@ -24,7 +24,7 @@ syslog S2 -level notice {
 
 syslog S3 -level notice {
     recv
-    expect ~ "[^:\\[ ]\\[${h1_pid}\\]: Health check for server be3/srv3 failed.+reason: Layer4 connection problem.+info: \"General socket error \\(Network is unreachable\\)\".+check duration: [[:digit:]]+ms.+status: 0/1 DOWN."
+    expect ~ "[^:\\[ ]\\[${h1_pid}\\]: Health check for server be3/srv3 failed.+reason: Layer4 connection problem.+info: \"General socket error \\(Network.* unreachable\\)\".+check duration: [[:digit:]]+ms.+status: 0/1 DOWN."
 } -start
 
 syslog S4 -level notice {