Description of problem:
If rpm-sign package is not installed and I try to run rpm --addsign I get a very confusing error:

# ls *.rpm
lcms-1.15-1.2.2.x86_64.rpm
# rpm --addsign lcms-1.15-1.2.2.x86_64.rpm 
rpm: lcms-1.15-1.2.2.x86_64.rpm: No such file or directory

If the rpmsign is now separately packed the rpm command should indicate the rpmsign binary is not available and not fail like this.

The error comes from execve I think:
execve("/usr/bin/rpmsign", ["/usr/bin/rpmsign", "--addsign", "lcms-1.15-1.2.2.x86_64.rpm"], [/* 26 vars */]) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=2512, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f8328d87000
read(3, "# Locale name alias data base.\n#"..., 4096) = 2512
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7f8328d87000, 4096)            = 0
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
write(2, "rpm: lcms-1.15-1.2.2.x86_64.rpm:"..., 59rpm: lcms-1.15-1.2.2.x86_64.rpm: No such file or directory
) = 59
exit_group(1)                           = ?

Version-Release number of selected component (if applicable):
rpm-4.9.1.2-1.el7

How reproducible:
100%

Steps to Reproduce:
1. rpm -e rpm-sign
2. wget a RPM_FILE
3. rpm --addsign RPM_FILE
  
Actual results:
Confusing error

Expected results:
rpm prints it cannot find rpmsign binary and this may be located in other package.

Additional info: