Add man page for missing hydra executables

Fixes #1897. This adds a simple man page for hydra_nameserver, hydra_persist,
and hydra_pmi_proxy. None of these man pages have any real information in them
as users shouldn't be using these executables directly.
Signed-off-by: Ken Raffenetti <raffenet@mcs.anl.gov>

src/pm/hydra/pm/pmiserv/Makefile.mk

@@ -37,3 +37,5 @@ libpm_la_SOURCES += pm/pmiserv/pmiserv_pmi.c \
 	pm/pmiserv/pmiserv_utils.c \
 	pm/pmiserv/common.c \
 	pm/pmiserv/pmi_v2_common.c
+
+doc1_src_txt += pm/pmiserv/hydra_pmi_proxy.txt

src/pm/hydra/pm/pmiserv/hydra_pmi_proxy.txt

+/*D hydra_pmi_proxy - Internal exectuable used by Hydra
+
+   Description:
+    This executable is designed to not be run directly by users, but to
+    support the Hydra process manager. As such, no documentation will be
+    provided here.
+
+D*/

src/pm/hydra/tools/bootstrap/persist/Makefile.mk

@@ -20,3 +20,5 @@ noinst_HEADERS +=                            \
 libhydra_la_SOURCES += tools/bootstrap/persist/persist_init.c \
 	tools/bootstrap/persist/persist_launch.c \
 	tools/bootstrap/persist/persist_wait.c
+
+doc1_src_txt += tools/bootstrap/persist/hydra_persist.txt

src/pm/hydra/tools/bootstrap/persist/hydra_persist.txt

+/*D hydra_persist - Internal executable used by Hydra
+
+   Description:
+    This executable is designed to not be run directly by users, but to
+    support the Hydra process manager. As such, no documentation will be
+    provided here.
+
+D*/

src/pm/hydra/tools/nameserver/Makefile.mk

@@ -11,3 +11,5 @@ hydra_nameserver_CFLAGS = $(AM_CFLAGS)
 hydra_nameserver_LDFLAGS = $(external_ldflags) 
 hydra_nameserver_LDADD = -lhydra $(external_libs)
 hydra_nameserver_DEPENDENCIES = libhydra.la
+
+doc1_src_txt += tools/nameserver/hydra_nameserver.txt

src/pm/hydra/tools/nameserver/hydra_nameserver.txt

+/*D hydra_nameserver - Internal executable used by Hydra
+
+   Description:
+    This executable is designed to not be run directly by users, but to
+    support the Hydra process manager. As such, no documentation will be
+    provided here.
+
+D*/