perf tests: Use shebangs in the shell scripts

Since the first line was used as a test identification, it needs to be
skipped by shell_test__description() function now.

Further notes from Hendrik:

It might be worth to note that adding the shebang is necessary to spot
them as scripts.

Using /bin/sh looks fine to.  Just briefly checked whether the scripts
contains some bash-specifics, which is not the case.

Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
LPU-Reference: 2127419430.57657104.1542836358464.JavaMail.zimbra@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/probe_vfs_getname.sh

@@ -1,3 +1,4 @@
+#!/bin/sh
 # Add vfs_getname probe to get syscall args filenames
 #
 # Arnaldo Carvalho de Melo <acme@kernel.org>, 2017

tools/perf/tests/shell/record+probe_libc_inet_pton.sh

@@ -1,3 +1,4 @@
+#!/bin/sh
 # probe libc's inet_pton & backtrace it with ping
 
 # Installs a probe on libc's inet_pton function, that will use uprobes,

tools/perf/tests/shell/record+script_probe_vfs_getname.sh

@@ -1,3 +1,4 @@
+#!/bin/sh
 # Use vfs_getname probe to get syscall args filenames
 
 # Uses the 'perf test shell' library to add probe:vfs_getname to the system

tools/perf/tests/shell/trace+probe_vfs_getname.sh

@@ -1,3 +1,4 @@
+#!/bin/sh
 # Check open filename arg using perf trace + vfs_getname
 
 # Uses the 'perf test shell' library to add probe:vfs_getname to the system